Oxetane ring, conformation

Substitution of alkyl and aryl groups on the oxetane ring, on the other hand, increases the barrier of the puckering vibration. 2-Methyloxetane and 3-methyloxetane are non-planar, existing as mixtures of stable equatorial and axial conformers at room temperature (79JST(56)157>. 

Cyclopropane analog " 98 showed microtubule disassembly inhibitory activity comparable with paclitaxel, but lower than docetaxel. The author thus demonstrated that the oxetane ring is not essential for the interaction of paclitaxel analogs with microtubules when the C-ring conformation is locked by cyclopropane, but the oxygen atom in the D ring of paclitaxel may participate in the stabilization of a dmg-tubulin complex. 

When a four-membered heterocycle is cis-fused on the side of another ring, as with syn-44, which we met in chapter 12, cyclisation of the syn-monotosylate 42 in base is very efficient as the, usually unfavourable, conformation 10 is now the only possible one and the nucleophile and electrophile are perfectly arranged 43 for cyclisation. This observation took on a new importance when the anti-cancer compound taxol was discovered as it also has a cis -fused oxetane.6... 

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